Journal of Colloid Science最新文献

Size and shape of micelles of Na and K salts of (tripentylmethyl)benzenesulfonic acid in n-heptane were determined from light scattering and sedimentation. These systems behave quite differently from most aqueous micellar systems, which entails special problems in the interpretation of the experimental results. The micelle size depends strongly upon soap concentration and temperature and upon the nature of the cation.

The behavior of the potassium sulfonate micelles can be reasonably described in terms of a model theory, which theory, however, does not hold for the sodium soap.

Partition coefficients (K_D = C_H2O/C_isooctane) below the critical micelle concentration have been determined for a homogeneous and normal (Poisson) distribution series of p, t-octylphenoxyethoxyethanols (OPE_1–10) in the system, isooctane-water, at 25°C. As the ethylene oxide (EO) chain length increases from 1 to 10, K_D increases by four orders of magnitude. The calculated standard free energy change (ΔG_EO⁰) of transport of 1 mole of ethylene oxide from the isooctane to the aqueous phase is −0.60 kcal. mole⁻¹ for single species OPE's. Assuming a Poisson distribution of molecular weights and weak interactions between OPE molecules of varying EO chain length, one can calculate to a good approximation the partition coefficients of normal distribution OPE's from the partition coefficients of single species OPE's. Similarly, one can calculate the molecular weight distribution and average molecular weight of a given OPE in both the isooctane and aqueous phases as a function of the phase volume ratio of isooctane and water. An order of magnitude estimate of the partition coefficients of normal distribution and single species OPE's can be made from appropriate c.m.c. data. A 35°C. temperature increase decreases the partition coefficient of single species OPE₉ by an order of magnitude. The corresponding standard enthalpy (ΔH°) and standard entropy (ΔS°) changes for the transfer of 1 mole of OPE₉ from the isooctane phase to the aqueous phase are −12.9 kcal. mole⁻¹ and −43 e.u., respectively. The partition coefficient of single species OPE₉ increases with increasing concentration at concentrations in excess of the onset of micellization.

A styrene copolymer with 2.3 mole % of methacrylic acid was modified by grafting short polycaprolactam side chains to the carboxyl residues. The creep and creep recovery was studied over a range of temperatures on graft polymers containing 20% dioctyl phthalate plasticizer. A sample in which the side chains contained on the average 5 caprolactam units was a rubber-like elastomer at 125°C., showing no evidence of an irreversible creep. This behavior was interpreted as due to the formation of a gel network by hydrogen-bonding between the polycaprolactam side chains. Covalent cross-linking could be excluded since the graft polymer was soluble in various solvent media. At higher temperatures the interpretation of the data was uncertain because of slow plasticizer loss and chemical degradation, but the molding behavior of the sample at 205°C. indicated that the gel structure had disappeared at that temperature.

CuS and As₂S₃ sols in N-methylacetamide have been prepared and have been purified by electrodialysis. Both sols were found to carry negative charges.

Flocculation values were determined using solutions of NaI and of CaCl₂ in NMA at 40°C. The experimental values for both sols were considerably higher than for similar systems in water.

As₂S₃ sols in NMA exhibit very unusual stability, showing no flocculation after three months.

The CuS sol was found to be inherently unstable in NMA and to dissolve in a few days. Coordination of NMA molecules around the Cu⁺⁺, ion and the very high dielectric constant of the medium may contribute to this behavior.

The liquid repellency to liquids of varying surface tensions was examined for a number of differently woven cotton fabrics that were treated with a fluorochemical textile finish.

Expressions for the liquid-solid and liquid-air interfaces per unit of macroscopic surface area have been derived and used to calculate the apparent surface contact angles. Comparison with experimental data has shown that these expressions are correct.

Liquid-yarn advancing contact angles have been obtained from measurements of the pressure required to force the liquid through the pores in the fabrics.

The abrupt drop of repelling performance for liquids of surface tension under 25 dynes/cm. is discussed in terms of textile structure and fiber surface.

The existence of two types of molecular, adsorbed water on the surface of precipitated silica has been confirmed. It has been shown that the physically adsorbed water gives a Type II isotherm and requires an activation energy of 6.6, 7.4, and 8.2 kcal./mole for its removal, on three different precipitated silica samples studied. The second type of water is probably H-bonded to SiOH groups and conforms to a Langmuir isotherm, requiring about 10 kcal. activation energy for its removal. The data are consistent with a bridged structure involving one water and two SiOH groups. The data suggest that past reports of water adsorption on silica surfaces have shown monolayer coverage to be complete at spurious partial pressures because the two types of water adsorption have not been clearly separated.

The hydrophile-lipophile balance (HLB) of liquid nonionic surface-active agents is linearly related to the measured heat of hydration by the relation $\text{HLB}\text{= 0.42Q + 7.5,}$ where Q = the heat of hydration in g.-cal./g. In the case of mixtures, this relationship represents a positive deviation from strictly additive behavior. A simple calorimetric arrangement for the determination of the heat of hydration is described.

Water-in-heptane emulsions were prepared containing 0.5 % by volume of Span 80 and water-in-benzene emulsions with 1 % of Span 85.

By measuring the centrifugation current, the electrokinetic mobility was determined for different concentrations of electrolytes (NaCl, BaCl₂, Ce(N0₃)₃, Na₂SO₄, and also HCl and KOH) in the aqueous phase.

The influence of the valency of the cations required a generalization of the equation for the electrokinetic mobility in the case of emulsions. This makes an evaluation of zeta potentials difficult.